Telephone conference calls are well-known in the art. Such calls are arranged so that a new party can be added to the conference by an existing person dialing out, and any of the existing parties can leave by hanging up. Some systems allow a new party to dial in to a call, but do not allow two existing multi-way calls to be merged into one, nor allow a single existing multi-way call to be split into two. These restrictions are partly due to the nature of existing PSTN equipment, and in particular the very limited degree of control information that can be exchanged with a conventional telephone. Furthermore merging and splitting have to be very carefully coordinated across the various nodes if they are to be successful.
More recently, multi-media conferencing facilities have been developed, which provide both video and voice connections (see, e.g. "Distributed Multiparty Desktop Conferencing System: MERMAID", by K. Watabe, S. Sakata, K. Maeno, H. Fukuoka, T. Ohmori, in "CSCW '90: Proceedings of the Conference on Computer-Supported Cooperative Work", 1990). A CCITT proposal (part of the T.12x draft standards) for a Multi-media Control Unit to handle multi-media conferencing imposes many of the same restrictions as currently exist for telephone conferences. This is partly due to the adoption of a relatively fixed, hierarchical structure, which centralizes control at a single node. A need exists for a call management system which does not suffer from such limitations.